You don't actually have to be in your mercury to trade with it. During the first 10 hours or so of your game the economy will be set to "easy mode" as their won't be many rival trading vessels and it should be easy to find stations that have close to full supply of product (means the cheapest buying price) and then sell it at a station which has none of that component(they will buy for maximum price) in the same sector or the sector next to it.

Some examples of this is the solar power plants in the Ore Belt sector (south of home of light) - you can buy ecells (price at 14 credits) and sell them to the Ore mines in the same sector for maximum price. At the same time once those ore mines are full of ore you can buy the ore and sell it in the sectors to the east and west which are full of weapons factories. Easy money.

Once you have some decent capital you will want to trade items that are more profitable like silicon wafers and eventually weapons and other ship components.